Ms. Wojcicki, in whose garage the company had its first offices, will leave her role leading ads and commerce to take over YouTube. Sridhar Ramaswamy, who had been sharing the ads role with Wojcicki, is expected to become the sole leader of the group, according to a person familiar with the matter.

Mr. Kamangar, another longtime executive who helped Google’s founders raise the company’s venture-capital investment, is expected to stay with the company, though his new role is unclear.

In a statement, Google CEO Larry Page credited Mr. Kamangar with building “a billion person global community curating videos for every possibility.” He said Ms. Wojcicki “has a healthy disregard for the impossible and is excited about improving YouTube.”

The YouTube leadership change was first reported by tech news site The Information.

YouTube is growing quickly. EMarketer estimates that it generated $5.6 billion of revenue in 2013, up from $3.7 billion in 2012.

Even so, the unit faces questions regarding its content strategy and the price of its ads, which have stayed below $10 per 1,000 viewers according to research firm TubeMogul. Producers of videos on YouTube say that at that level they struggle to make enough money, especially after splitting giving YouTube its typical 45% cut.

Note: This post has been updated to include the statement from Mr. Page.